Bertrand SIMONNET | e6cd738 | 2015-07-01 15:39:44 -0700 | [diff] [blame] | 1 | .\" ************************************************************************** |
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Elliott Hughes | 1ef06ba | 2018-05-30 15:43:58 -0700 | [diff] [blame] | 23 | .TH CURLOPT_WRITEFUNCTION 3 "February 03, 2016" "libcurl 7.60.0" "curl_easy_setopt options" |
Elliott Hughes | 82be86d | 2017-09-20 17:00:17 -0700 | [diff] [blame] | 24 | |
Bertrand SIMONNET | e6cd738 | 2015-07-01 15:39:44 -0700 | [diff] [blame] | 25 | .SH NAME |
| 26 | CURLOPT_WRITEFUNCTION \- set callback for writing received data |
| 27 | .SH SYNOPSIS |
| 28 | .nf |
| 29 | #include <curl/curl.h> |
| 30 | |
| 31 | size_t write_callback(char *ptr, size_t size, size_t nmemb, void *userdata); |
| 32 | |
| 33 | CURLcode curl_easy_setopt(CURL *handle, CURLOPT_WRITEFUNCTION, write_callback); |
| 34 | .SH DESCRIPTION |
| 35 | Pass a pointer to your callback function, which should match the prototype |
| 36 | shown above. |
| 37 | |
| 38 | This callback function gets called by libcurl as soon as there is data |
| 39 | received that needs to be saved. \fIptr\fP points to the delivered data, and |
| 40 | the size of that data is \fIsize\fP multiplied with \fInmemb\fP. |
| 41 | |
| 42 | The callback function will be passed as much data as possible in all invokes, |
| 43 | but you must not make any assumptions. It may be one byte, it may be |
| 44 | thousands. The maximum amount of body data that will be passed to the write |
| 45 | callback is defined in the curl.h header file: \fICURL_MAX_WRITE_SIZE\fP (the |
| 46 | usual default is 16K). If \fICURLOPT_HEADER(3)\fP is enabled, which makes |
| 47 | header data get passed to the write callback, you can get up to |
| 48 | \fICURL_MAX_HTTP_HEADER\fP bytes of header data passed into it. This usually |
| 49 | means 100K. |
| 50 | |
| 51 | This function may be called with zero bytes data if the transferred file is |
| 52 | empty. |
| 53 | |
| 54 | The data passed to this function will not be zero terminated! |
| 55 | |
| 56 | Set the \fIuserdata\fP argument with the \fICURLOPT_WRITEDATA(3)\fP option. |
| 57 | |
| 58 | Your callback should return the number of bytes actually taken care of. If |
| 59 | that amount differs from the amount passed to your callback function, it'll |
| 60 | signal an error condition to the library. This will cause the transfer to get |
| 61 | aborted and the libcurl function used will return \fICURLE_WRITE_ERROR\fP. |
| 62 | |
| 63 | If your callback function returns CURL_WRITEFUNC_PAUSE it will cause this |
| 64 | transfer to become paused. See \fIcurl_easy_pause(3)\fP for further details. |
| 65 | |
| 66 | Set this option to NULL to get the internal default function used instead of |
| 67 | your callback. The internal default function will write the data to the FILE * |
| 68 | given with \fICURLOPT_WRITEDATA(3)\fP. |
| 69 | .SH DEFAULT |
| 70 | libcurl will use 'fwrite' as a callback by default. |
| 71 | .SH PROTOCOLS |
| 72 | For all protocols |
| 73 | .SH AVAILABILITY |
| 74 | Support for the CURL_WRITEFUNC_PAUSE return code was added in version 7.18.0. |
| 75 | .SH RETURN VALUE |
| 76 | This will return CURLE_OK. |
| 77 | .SH EXAMPLE |
| 78 | A common technique is to use this callback to store the incoming data into a |
| 79 | dynamically growing allocated buffer. Like in the getinmemory example: |
Alex Deymo | 8f1a214 | 2016-06-28 14:49:26 -0700 | [diff] [blame] | 80 | https://curl.haxx.se/libcurl/c/getinmemory.html |
Bertrand SIMONNET | e6cd738 | 2015-07-01 15:39:44 -0700 | [diff] [blame] | 81 | .SH "SEE ALSO" |
| 82 | .BR CURLOPT_WRITEDATA "(3), " CURLOPT_READFUNCTION "(3), " |